Manufacture of artificial silk and by-product recovery therefrom



Aug. 25, 1936. A. J. L. MORITZ ET AL 20,079

MANUFACTURE OF ARTIFICIAL SILK AND BYAPRODUCT RECOVERY THEREFROMOriginal Filed Dec. 26, 1934 ATTORNEY Reissued Aug. 25, 1936 UNITEDSTATES PATENT OFFICE MANUFACTURE OF ARTIFICIAL SILK AND BY-PRODUCTRECOVERY THEREFROM Adrian J. L. Moritz and Jan J. Schilthuis, Enka, N.C., assignors to American Enka Corporation, Enka, N. 0., a corporationof Delaware Claims. (01. 18-54) The present invention relates to themanufacture of artificial silk in such a manner that the by-productsformed during the said manufacture are rendered recoverable, and arerecovered by 5 an improved process and apparatus therefor. Moreparticularly, the invention is concerned with the recovery of carbondisulphide during the treatment of artificial silk after it has beenextruded in the form of threads and collected in package form in a wetcondition.

During the normal manufacture of viscose, cellulose is reacted withalkali to form the alkali cellulose. After aging the alkali cellulose tothe desired extent, it is brought into contact with carbon disulphide toform by a combination reaction, alkali cellulose xanthate, and this saidcompound is then formed into what is termed theviscose solution bydissolving the same in a dilute alkaline solution. The spinning periodof 20 the viscose solution follows the preparation thereof, and thisinvolves extruding and coagulating the solution to form threadstherefrom. In this procedure the alkali cellulose xanthate is decomposedwith the formation of cellulose, carbon disulphide, hydrogen sulphide.and a small portion of free sulphur. A small part of the carbondisulphide and a large part of the hydrogen sulphide is carried awayduring the spinning operation intermixed with ventilated air at a point80 above the spinning machines. However, the largest proportion of thecarbon disulphide is retained within the thus formed and collectedartificial silk.

, In the usual processes employed in the manufacturing of artificialsilk, after the cellulosic solutions have been forced through the minuteopenings in the spinning nozzles to form threads or filaments and arecoagulated by being passed through the acid spinning baths, the threadsor filaments thus formed are wound on collecting devices such asbobbins, spools, cops, perforated carriers and the like; or as analternative procedure the threads or filaments are spun into centrifugalspinning pots to form cakes. After such manipulations of the threadincluding the formation of the packages, it has been found necessary toextract impurities existing in the packages by washing, desulphurizingand drying the same in such a manner as to effecta uniform contractionof the thread throughout all parts thereof. To accomplish this in apractical manner, the packaged thread has been rewound from the bobbinor pot into skein form, and thereafter vthe thread in this form has beensubjected to washing and desulphurizing by the drip wash method. Thewashing of the skeins of thread involved not only the removal of theimpurities present therein, but also caused the removal of theby-products which were lost by being conducted away through the wastedrain pipes pro- 5 vided for carrying off the treating solutions, orsome of the more volatile by-products were passed off in the form ofgases through exit pipes into the surrounding atmosphere.

The recovering of the carbon disulphide during 10 the process ofmanufacture is of extreme importance and, so far as we are aware, thishas not been heretofore accomplished. That the process including therecovery of carbon disulphide is of extreme importance will be readilyappreciated 15 when it is borne in mind that carbon disulphide is theprincipal reactant employed during the manufacture of viscose. Thisproduct is very expensive and owing to its extreme inflammability isdiificult .to handle particularly in transportation. 20 Not only is therecovery practical from the standpoint of economy, but it is importantto prevent the uncontrolled introduction of the carbon disulphide intothe surrounding atmosphere with the resultant grave fire hazard. Then,too, this gas 5 is also very obnoxious.

It is therefore an object of the present invention to provide a methodof manufacturing artificial silk in which by-products formed during themanufacture of the artificial silk are rendered 30 recoverable.Additionally, the invention contemplates the provision of a system inwhich the present method may be practiced.

Another object of this invention is the provision of an improvedapparatus for the manu- 35 facture of artificial silk in whichrecoverable lay-products formed during the manufacture are maintainedconfined at all times.

Still another object of this invention is the carrying out of a processby means of the said 40 apparatus in which carbon disulphide, issubjected to such conditions as to effect its separation and recovery.

Other objects and advantages of the invention will be apparent from thefollowing detailed de- .45 scription when considered in connection withthe accompanying drawing, wherein:

The figure illustrates diagrammatically a system suitable for treatingpackages of artificial silk and the simultaneously separating and re-5.0 covery of the by-products during such treatment.

In referring to the drawing in detail, the reference numeral ldesignates a vacuum wash tank for containing a plurality of artificialsilk packages 2 positioned in any convenient manner such 65 as by beingplaced in juxtaposition over perforations 3 located within the bottom 4of the tank. A water supply pipe is shown at 5 for introducing waterinto the tank I and a suction pipe line B is located below and connectedwith the water and gas exhaust space I existing by virtue of the doublebottomed construction of tank I.

The suction pipe line 6 extends into a separator tank 8 and a valvemeans 9 is located within the pipe line 6 for shutting off the water andgas mixture at will. The separator tank 8 is provided with an exhaustWater suction pipe I0 connected to a water pump I I which is arrangedfor withdrawing the water containing waste materials and for exhaustingthe same through any suitable means.

Connected to the top of the separator tank is a. pipe I2 which leads toa vacuum reserve tank I3. The vacuum tank is adapted to maintain apredetermined vacuum on the recovered byproducts contained within thesaid tank. A main vacuum pump or pumps I 4 is positioned at a suitablepoint between the vacuum reserve tank and an absorption apparatus I5,and this vacuum pump is connected by a piping arrangement I6 while thevacuum pump is connected on its other side with the absorption apparatusby a piping arrangement II.

The above description of the recovery system explains the function ofthe various elements when employed in combination to carry out thepresent process.

In operation, it can be seen that the present process is especiallyadaptable to the vacuum washing system applied to packages of artificialsilk. In such a system the packages whether in bobbin form or in cakesare transferred to the washing tanks immediately after they have beenextruded in the form of filaments and wound or spun into packages. Aswas stated above, the vapors from the freshly wound packages contain alarge proportion of carbon disulphide ranging from 15 to 40% by volume.These packages are placed within the wash tank over openings within thebottom of the tank and sealed. The tank is thereupon filled with waterwhich is drawn through the packages from the outside to the inside as aresult of the suction effect created by the vacuum within the cakes, andthe carbon disulphide and water containing other impurities is drawninto a separator tank.

It is to be understood that if it is desirable, the washing liquid maybe introduced into the space defining the interior of the packages anddrawn to the exterior thereof by the same vacuum means. In fact, themanner in which the packages may be washed can be accomplished in anumber of ways, just so the wash water and byproducts are confined tothe extent that they may be separated by subsequent practicaloperations.

As the entire system is under a vacuum, the carbon disulphide will notbe .dissolved by the water to any appreciable degree, and accordingly,substantially all of the carbon disulphide is withdrawn through the topof the separator tank while the water containing waste material may bepumped from the bottom of the said separator tank in any suitablemanner.

The carbon disulphide containing a small amount of hydrogen sulphide andmoisture is maintained at a practical working temperature and drawn bymeans of the vacuum pump into a reserve tank to be subsequently purifiedfor reemployment in the manufacture of artificial silk. The purificationof the carbon disulphide may be carried out in any one of a number ofknown operations.

It has been found very practical to purify and recover the carbondisulphide by means of absorbing the same through oils and subsequentlysteaming the carbon disulphide out of the oil. However, it might bedesirable to recover and purify the carbon disulphide by means ofcharcoal or other solid absorbent materials or by absorbing the same inother types of solvents. Furthermore, recovery of carbon disulphide maybe effected by partial condensation when the partial pressure of carbondisulphide in the mixture is sufficiently high.

Whereas the invention has been described as applicable to the systemshown in the drawing,

it is to be understood that the scope of the in vention shall not belimited thereto in view of the fact that it is the intention to includeall processes whereby carbon disulphide and other volatile by-productsresulting from the manufacture and treatment of artificial silk arerendered recoverable by the said silk manufacture in which the saidby-products are subsequently recovered in any practical manner. 7

We claim:

1. In the manufacture of artificial silk from viscose solutions whereinthe solutions are extruded to form threads and the like and directlycollected in package form, the process which comprises washing thefreshly spun packages of artificial silk with an aqueous solution toelimi nate the impurities and slightly soluble volatile by-productsformed during the manufacture of the artificial silk, removing the thuscharged solution to a separating zone, effecting the separation of thevolatile by-products from the solution containing the other impurities,passing the separated volatile by-products into a reserve zone andfinally purifying the by-products while at all times maintaining themconfined, whereby substantially all of the by-products contained in thesilk are recovered and adapted for reemployment in the manufacture ofartificial silk.

2. In the-manufacture of artificial silk from viscose solutionswherein-the solutions are extruded to form threads and the like anddirectly collected in package form, the process which comprises washingthe freshly spun packages of artificial silk with an aqueous solution toeliminate the impurities and CS2 formed during the manufacture of theartificial silk, removing the thus charged solution to a separatingzone, effecting the separation of the CS2 from the solution containingthe other impurities while under a pressure below atmospheric, passingthe separated CS2 into a reserve zone and finally purifying the CS2while at all times maintaining it confined, whereby substantially all ofthe CS2 contained in the silk is recovered and adapted for 'reemploymentin the manufacture of artificial silk.

3. In the manufacture of artificial silk from viscose solutions whereinthe solutions are extruded to form threads and the like and directlycollected in package form, the process which comprises washing thefreshly spun packages of artificial silk with an aqueous solution bydrawing the same through the packages from'the exterior to the interiorthereof by vacuum to take out the CS2 formed during the manufacture ofthe artificial silk, removing the thus charged solution in toto to aseparating zone, evacuating the space above the charged solution tothereby effect a separation of the CS2 from the waste liquid,controlling the separating operation by passing the CS1 into a reservezone which permits the maintenance of a predetermined pressure belowatmospheric to be imposed upon the system, and finally subjecting theconfined CS2 to the absorbent action of a suitable agent to purify thesame, whereby substantially all of the CS: contained in the silk isrecovered and adapted for reemployment in the manufacture of artificialsilk.

4. In the manufacture of artificial silk from viscose solutions whereinthe solutions are extruded to form threads and the like and directlycollected in packageform, the process which comprises washing thefreshly spun packages of artificial silk with an aqueous solution toeliminate the impurities and slightly soluble volatile by-productsformed during the manufacture of the artificial silk, removing the thuscharged solution to a separating zone, effecting the separation of thevolatile by-products from the solution containing the other impurities,and finally purifying the by-products while at all times maintainingthem confined, whereby substantially all of the lay-products containedin the silk are recovered and adapted for reemployment in themanufacture of artificial silk.

5. In the manufacture of artificial silk from viscose solutions whereinthe solutions are extruded to form threads and the like and directlycollected in package form, the process which comprises washing thefreshly spun packages of artificial silk with an aqueous solution toeliminate the impurities and CS2 formed during the manufacture of theartificial silk, removing the thus charged solution to a separatingzone, effecting the separation of the CS2 from the solution containingthe other impurities while under a pressure below atmospheric andfinally purifying the CS2 while at all times maintaining it confined,whereby substantially all of the CS2 contained in the silk is recoveredand adapted for reemployment in the manufacture of artificial silk. 20

ADRIAN J. L. MORITZ. JAN J SCHILTHUIS.

